Antimicrobial susceptibility and the in vitro postantibiotic effects of vancomycin and ciprofloxacin against Bacillus cereus isolates

Background: Vancomycin and ciprofloxacin were often used in the therapy of infections associated with Bacillus cereus.

Methods: Four B. cereus food and clinical isolates were chosen for determination of time–kill curves and postantibiotic effects (PAE) of ciprofloxacin and vancomycin.

Results: According to the minimum inhibition concentration (MIC), breakpoints defined by CLSI for Staphylococcus spp. were all four strains intermediate for vancomycin (MIC?=?4?μg/ml) and sensitive to ciprofloxacin (MIC?=?0.2?μg/ml) except the strain Bc63 resistant to the last antimicrobial (MIC?=?1.6?μg/ml). The lowest CFU values of tested strains were reached after 3–5?hours of exposure to 4?× MIC of vancomycin, and after 6–7?hours exposure to 10?× MIC of ciprofloxacin. The maximum reduction of the CFU in the presence of vancomycin and ciprofloxacin was about 2.46 log₁₀ and 2.48 log₁₀, respectively. The average duration of the PAE of vancomycin and ciprofloxacin was 0.94 and 1.60?hours, respectively. The statistically significant differences between PAEs induced with 3?× MIC, 4?× MIC and 8?× MIC of vancomycin were observed (P?Conclusions: The differences in PAE duration were strain and antimicrobial dependent.